In this assignment, the major point of discussion varies around aircraft instruments, their operation and construction along with the health and safety precautions when servicing or operating them. In addition, a test section should also be explained. The first section talks about two specified instruments and their explanation along with the reason for monitoring them in general. The second section will hopefully explain the safety precautions required while servicing or operating aircraft instruments in general. Last but not least, the final section should show a test with its explanation.
Section 1:
a) Aircraft instruments are very important to make flight easier and more convenient. As aircrafts become bigger, it becomes more difficult to see through especially in the air. So basically instruments are there to ease the process of flying around and minimize the possibilities of unwanted accidents. I will start off with the Altimeter as my first chosen instrument.
An altimeter is a common instrument for most aircrafts as it measures the atmospheric pressure displaying it in feet terms. In other words, the distance of the aircraft, in height, from sea level is called the altitude (i.e. height) and the altimeter measures this distance. There are two types of altimeter to keep in mind. A sensitive altimeter and a non sensitive altimeter. The non-sensitive altimeter is less common and uses only one pointer while the sensitive altimeter uses three separate pointers and gives a more accurate reading and indication. So what is the difference? Imagine an analogue clock with numbers from 0 to 9. The non-sensitive meter has one pointer for this clock and each number is multiplied by 1000 so if the pointer is at 6 then the altitude is 6000 meters in height. However, for more modern aircrafts, a sensitive altimeter is there with three pointers, the longest pointers points at the numbers multiplied by 100, the medium in length pointer points at numbers multiplied by 1000 and the shortest pointer points at numbers multiplied by 10,000. So for example, if the longest pointer is pointing at 5, the medium pointer is pointing at 7 and the shortest pointer is pointing at 3 then the altitude of the aircraft is 37,500 feet up in the air.
The principle of operation is simple, the sensing element is a partially evacuated capsule and a leaf spring is used to prevent it from collapsing. The capsule is mounted within a case that is almost sealed excluding the feed of static pressure. So in case of a decrease in the static pressure, the spring will become strong enough to expand the capsule, thus the movement of expansion is fed through a system of linkage that causes a needle to rotate over he altimeter dial. However, on the other hand, if the static pressure increases, the process is reversed as the capsule is caused to contract against the spring so the needle or pointer will move in the opposite direction. This was the basic operation of a basic altimeter. In a servo altimeter type (most popular and modern), the expansion or contraction of the capsule moves one end of the bar that is concentrated at its centre. This bar is called the �I� bar in this case because if its shape and the coils are wrapped on a nearby E shape structure to produce and pass alternate current. After this process, the air gaps between the I bar and the outer arms of the E structure will no longer be equal, thus no voltages will be induced. Servo altimeters are digitally displayed and the most accurate as they are less exposed to errors unlike the previous two analogue altimeters.
The second instrument I decided to explain and talk about is the Vertical Speed Indicator as it has something in common with the altimeter as both measures changes of static pressure. However, rather than showing the altitude, it indicates the rate of climb and descent of the aircraft. Its units are in feet per minute.
The basic principle of operation is somewhat like the altimeter as a capsule inside a sealed case is fed with static pressure that also feeds the inside of the case via a choke that permits changes of static pressure to pass only after a delay. When the aircraft climbs or descends, the consequent change of static pressure will be felt by the capsule instantly, but the change will reach the inside of the case only after a slight delay. During this slight delay, the capsule will contract (in case of a climb) or expand (in case of a descend) in response to the pressure difference inside the case. The movement of the capsule is fed through linkages to cause the needle to move over a calibrated dial. So it can be said that the faster the climb or descent rate, the greater will be the movement of the capsule and therefore the needle. The instrument dial usually has a logarithmic scale to give greater clarity at low rates of climb and descend.
b) Aircraft systems are delicate instruments that must be worked with carefully. Such instruments must be regulated and monitored carefully with a careful eye kept on them. For example the compass may become inaccurate over a particular time so should be updated regularly. The black box for another example, while a self sustained system, must be taken care off to avoid damage being inflicted upon it. We must keep in mind that the black box re-records its data so it must be monitored carefully. In other words, we must keep regular monitoring over aircraft instruments to keep things in line.
Section 2:
Health and safety is a major role while working in the workshop or on an aircraft. In this section we will concentrate on the safety precautions while working on aircraft instruments but at the same time, we should not forget the basic rules. General health and safety concepts and procedure includes:
1) Overalls for body protection as they are properly made in one piece.
2) Goggles for eye protection that must be worn when working with chemicals and other materials that may harm the eye.
3) Boots must be worn at all times for feet protection. Special workshop boots are supplied.
4) Ear defenders for ear protection must be worn when dealing with loud noises.
5) Helmet for head protection must be worn when working under the aircraft or when there is a risk of something falling from top.
6) Gloves for hand protection must be worn when dealing with chemicals, sharp objects, hot or cold materials, etc.
The six important and common workshop safety procedures listed above are known as personal protective equipments. However, when dealing with instruments, the following should be taken into account.
1) The operating engineer should be fully trained to work in his majority.
2) All powers must be switched off and a tag attached for warning other members that the power is switched off due to a personnel currently working on an instrument or equipment.
3) Before the power is switched off, visual check for making sure that no one is already working on the aircraft must be made.
4) The operating engineer must have his full equipments with him numbered and ready to use.
5) The tools must be numbered so that anything that goes inside the aircraft does not stay there without a purpose.
6) Make sure that the aircraft parts are in the right position that suits your work.
7) If the part needs configuration, no one should be near that part to avoid hazards.
8) The workshop is not a playing ground and everything is counted on you.
9) Make sure that all jewelry is removed before working on the aircraft and the clothes you are wearing are tight and not torn away to avoid it being caught in any machinery.
10) Give previous notice to teammates and other personnel that your work will be in progress soon.
11) When dealing with certain instruments such as the Speed Indicator, no one should touch the pitto as it will be very hot. A sign should be there to indicate that.
12) When working with other instruments such as the radar, the aircraft should be in a free space and no one within a 30 meter rang of the plane. Stands and pos signs should be there to warn people as harmful signal are produced at this stage.
13) When removing any instrument off the aircraft, a replacement instrument should be instantly prepared to be replaced and the old one should be fitted in the new ones box and sent for repair.
(Continued on next page)
